This invention relates to compositions useful in the microelectronics industry for cleaning semiconductor wafer substrates. Particularly, this invention relates to alkaline stripping or cleaning compositions containing bath stabilizing agents that are used for cleaning wafers having tungsten metal lines and vias by removing contaminants without damaging the integrated circuits.
Interconnect circuitry in semiconductor circuits consists of conductive metallic circuitry surrounded by insulating dielectric material. In the past, silicate glass vapor-deposited from tetraethylorthosilicate (TEOS) was widely used as the dielectric material, while alloys of aluminum were used for metallic interconnects.
Demand for higher processing speeds has led to smaller sizing of circuit elements, along with the replacement of TEOS and aluminum alloys by higher performance materials. Aluminum alloys have been replaced by copper or copper alloys due to the higher conductivity of copper. TEOS and fluorinated silicate glass (FSG) have been replaced by the so-called low-k dielectrics, including low-polarity materials such as organic polymers, hybrid organic/inorganic materials, organosilicate glass (OSG), and carbon-doped oxide (CDO) glass. The incorporation of porosity, i.e., air-filled pores, in these materials further lowers the dielectric constant of the material.
During dual-damascene processing of integrated circuits, photolithography is used to image a pattern onto a device wafer. Photolithography techniques comprise the steps of coating, exposure, and development. A wafer is coated with a positive or negative photoresist substance and subsequently covered with a mask that defines patterns to be retained or removed in subsequent processes. Following the proper positioning of the mask, the mask has directed therethrough a beam of monochromatic radiation, such as ultraviolet (UV) light or deep UV (DUV) light (≈250 nm or 193 nm), to make the exposed photoresist material more or less soluble in a selected rinsing solution. The soluble photoresist material is then removed, or “developed,” thereby leaving behind a pattern identical to the mask.
Thereafter, gas-phase plasma etching is used to transfer the patterns of the developed photoresist coating to the underlying layers, which may include hardmask, interlevel dielectric (ILD), and/or etch stop layers. Post-plasma etch residues are typically deposited on the back-end-of-the-line (BEOL) structures and if not removed, may interfere with subsequent silicidation or contact formation. Post-plasma etch residues typically include chemical elements present on the substrate and in the plasma gases. For example, if a WN hardmask is employed, e.g., as a capping layer over ILD, the post-plasma etch residues include tungsten-containing species, which are difficult to remove using conventional wet cleaning chemistries. Moreover, conventional cleaning chemistries often damage the ILD, absorb into the pores of the ILD thereby increasing the dielectric constant, and/or corrode the metal structures. For example, buffered fluoride and solvent-based chemistries fail to completely remove WN and W-containing residues, while hydroxylamine-containing and ammonia-peroxide chemistries corrode metal lines such as, for example, copper or tungsten.
In addition to the desirable removal of tungsten-containing hardmask and/or tungsten-containing post-plasma etch residue, additional materials that are deposited during the post-plasma etch process such as polymeric residues on the sidewalls of the patterned device and copper-containing residues in the open via structures of the device are also preferably removed. To date, no single wet cleaning composition has successfully removed all of residue and/or hardmask material while simultaneously being compatible with the ILD, other low-k dielectric materials, and metal interconnect materials.
The integration of new materials, such as low-k dielectrics, into microelectronic devices places new demands on cleaning performance. At the same time, shrinking device dimensions reduce the tolerance for changes in critical dimensions and damage to device elements. Etching conditions can be modified in order to meet the demands of the new materials. Likewise, post-plasma etch cleaning compositions must be modified. Importantly, the cleaner should not damage the underlying dielectric material or corrode metallic interconnect materials, e.g., copper, tungsten, cobalt, aluminum, ruthenium, and silicides thereof, on the device.
Towards that end, it is an object of the present invention to provide improved aqueous compositions for the selective and effective removal of tungsten-containing post-plasma etch residue, polymeric sidewall residue, copper-containing via residue and/or tungsten-containing hardmask layers from microelectronic devices, said compositions being compatible with ILD and metal interconnect materials.
It is another object of the present invention to provide improved aqueous compositions having an extended bath-life relative to conventional peroxide-containing cleaning compositions.